Orthodontic brackets attached to teeth transmit forces, such as produced by an archwire, to move the teeth. Brackets usually contain an archwire slot for reception of the archwire. Orthodontic brackets today are typically bonded to a tooth or welded to an orthodontic band that is cemented to the tooth.
Brackets commonly use tie wings that project upwardly and downwardly in pairs at the top and bottom of the installed bracket, respectively. These wings permit the archwire to be held within the archwire slot of the bracket by means of a twisted wire (ligature) or an elastomeric o-ring. Currently there are varieties of brackets that are self-ligating. These self-ligating brackets have taken several forms.
U.S. Pat. No. 5,094,614 to Wildman, issued Mar. 10, 1992, discloses a sliding closure that engages the front of the archwire. The closure is recessed from the front or anterior surfaces of the disclosed bracket. These sliding closures are also found in U.S. Pat. No. 2,549,528 to Russell, U.S. Pat. No. 2,671,964 to Russell et al. and in U.S. Pat. No. 3,131,474 to Johnson. Sliding closures require the archwire also to be recessed within the archwire slot before the closure can be moved over the archwire making it very difficult for the user to visually confirm that the archwire is properly seated within the archwire slot. A conventional bracket has a visual front surface adjacent to the archwire slot making it easy to see if the archwire is seated in the archwire slot. This is not true in the recessed sliding closures. The actual archwire slot surface is beneath the sliding closure. Damon solved this problem in U.S. Pat. Nos. 5,275,557 (Jan. 4, 1994), 5,429,500 (Jul. 4, 1995) and 5,466,151 (Nov. 14, 1995).
An achievement of these patents is a ligating slide within a bracket that maintains the normal features of protruding tie wings or lugs and a closure in the form of a ligating slide that can complete a continuous tube surrounding the archwire when the closure is in a closed position. This can be achieved in a Siamese or twin bracket configuration without covering or interfering with projecting extensions on the bracket.
Pletcher, U.S. Pat. No. 5,322,435, discloses a locking slide member that is flat and guided by upright slots formed along both sides of the bracket and spanning the archwire slot thereby obscuring visual access to the critical corners of the archwire slots at the side edges of the bracket. Without this visual access being clear, one installing an archwire within a bracket cannot be certain as to proper seating of an archwire within the archwire slot before the slide cover is moved to a closed position. No tie wings or lugs are included in the illustrated bracket forms.
There is a modern esthetic requirement that the brackets be small. A drawback of many self-ligating brackets the locking covers increase the size of the bracket.
Damon, U.S. Pat. No. 6,071,118, discloses a sliding cover which gives visual access to the archwire slot, but have achieved the enclosure of the sliding cover by thickening the bracket in the gingival area
A sliding spring cover, a hinged locking cover, a rotary sliding cover, a ball type rotatable cover etc. have been disclosed in different U.S. Patents. “Activa” produced by A Company, “Speed” and “Edgelock” produced by Ormco Corporation, and others are typical examples of ligature-less brackets that are commercially available.
Of all these different locking means a sliding closure has been considered desirable because it can be easily manipulated and it reduces the time required for opening and closing of the arch wire slot during periodic adjustments of the arch wire and provides more precise control of the archwire. There are other means that are more complex and difficult and expensive to manufacture. Springs used as locking means are not strong enough to hold the arch wire into the slot.